1. Field of the Invention
The present invention relates to a sheet stacking apparatus and an image forming apparatus.
2. Description of the Related Art
A sheet stacking apparatus is known in which by aligning sheets that are stacked on a sheet stacking portion by a side aligning member, the alignment in a width direction crossing a conveying direction of the sheet is improved. Due to the fact that alignment processing is conducted by the side aligning member so as to align sheet edge portions in the width direction every time a sheet is stacked, the aligned state of sheets P on the sheet stacking portion is improved.
However, in such a conventional sheet stacking apparatus, an aligning operation with respect to sheets that are stacked on the sheet stacking portion is to be conducted only with respect to the width direction of the sheets, so that misalignment in the sheet conveying (discharging) direction cannot be corrected. To further improve the alignment of the stacked sheets, the alignment in the sheet conveying direction needs to be done in addition to that in the width direction.
Here, to correct a misalignment in the sheet conveying direction of the sheet, for example, it is conceivable that a leading edge stopper configured to control a leading edge position of the sheet having been stacked, as is a side aligning plate, is moved in the direction opposite to the sheet conveying direction to align the sheet every time a sheet is stacked.
In Japanese Patent Application Laid-Open No. H11-228033, an apparatus is described in which there is provided a sheet tray, a side guide regulating the position of the side edge portion of a sheet, and an end guide regulating the position of the end edge portion of the sheet. In this apparatus, every time the sheet is conveyed onto a sheet tray, both the side guide and the end guide are moved from the standby position to a position regulating the sheet. Furthermore, it is constructed such that in the state in which the side guide is located in a position of regulating the sheet, the end guide is moved to the position of regulating the sheet. In addition, the side guide and the end guide are constructed so as to start to move simultaneously from the position of regulating the sheet to the standby position.
In Japanese Patent Application Laid-Open No. H11-228033, only after the side guide and the end guide have returned to respective standby positions, can the next sheet be conveyed to the sheet tray. Therefore, in Japanese Patent Application Laid-Open No. H11-228033, it is difficult to discharge sheets at high speed, resulting in a low productivity.